Hydrocarbon synthesis plant



June 12, 1951 A. QVOORHIES, JR., ETAL 2,5

HYDROCARBON SYNTHESIS PLANT Filed Sept. 15, 1948 Patented june 12, 1951Krebs, East Batonv Rouge, La, assignors to Standard Oil Devlopment"Commun orpoatio of De a are Application September 15, 1948,.Serial No. 49A26 7 filairns. ,(ol. 260449.6)

i V The present in-vention relates to the synthesis of hydrocarbons from1 carbon oxides and hydro gen in the presence ofsuitable catalysts The:invention relates more particularly to a-process for obtaininghighyields o-f normally liquidhydrocarbonsboiling-withinthe gasoline andDiesel oilrange and concomitantly retarding excessive catalyst 1 oulingand disintegration.

The synthesis ofhydrocarbons and other valuable products. from gasmixtures containingvarious proportions-oi hydrogen and carbon oxides,particularly carbon monoxide, both in fixed bed-as well as in densephase fluid catalyst oper ation is well-known inthe art. The characterandquality of the synthesis product depends largely onthe temperatures,pressures, Hz/CO ratios ofthefeed -gas,--and the nature of the catalystused, the latter being usually an iron group.

metalcatalyst promoted-with such promoters as various alkalimetal-compounds, rareearth metal oxides, magnesia, alumina, etc.,inamounts of about 05-10%. Thus cobalt catalysts promoted with thoriaand/or magnesia have been used at relatively-low pressures of about 1575 p. s. i. g.-

and relatively low temperatures of about 350'- 450" F. and high Hz/COratio of 2 or more .toproduce a substantially saturated hydrocarbonmaterial from which valuable Dieselfuels, lubrieating; oils and waxesmay be obtained. Irontype catalysts, usually promoted with a suitablealkali metal compound, such as carbonates, halides, etc. of potassiumorsodiummay. :be usedin combination with relatively high pressures, upto 600?? 00p. sting. andtemperatures of4503-750 EL,

andlower Hz/COratios generally not above 2, to

produce. predominantly. unsaturated materialfrom which large proportionsof highoctane motor fuels may be recovered.- w

While it has thus been possible to obtain high octane motor fuels ingood yields bythisprocess,

it has also-been ioundthat operations under conditions that favorgoody-ields ofusefulii. e.

he c taly t arben dia tit n and the e ency'of catalyst particles todisintegrate, as a result of the carbon formation and deposit ion.arbm-deres -tiw. cat di in e i n hot only cut down product yield'throughpoor fluidization or" the catalyst, excessive fines formationagglomeration, but produce conditions ecir n shut iers t h 5.151951%? Ithas heretofore been found that the tendency er c rb nace u a ie f b'deri i -on h ca alyst and er talysts b' nt e ate-m r b relat gto the age ofth" ca yst and to'certain creatin v able T i is nbw h t'relaany r sh ynte is tat i e to' ed-er arter a a lihtta'r ie r ha datayst hat a e e he's stm r a relatively larger perio" of'tim' It is also known that thecarbon formation 'ten 'ncisand than acteristics of catalyst can .ueu uc1d'and' minimized to a considerable extent by increasing 9, 1 P, Q3 bfiff li 1 1 fi d find l b 'th hydrocarbon 'synth sis none." Thus, typicalexp erimental data he eshovkn that," at a hydrogen partialpressure ofbout 150 p. 'Is.i., an iron synthesis.cata 1yst,isuch as an alkali metalpromoted pyrites-ash catalyst, willyild, when it'has an average age, orresidence time under synthesisv conditionsof 5n"'11'ours,'.abourrsj rambf cari- Icon/m I-IzY-l-CO consumed? the average catalyst age hasincreased "to 20Qliours the carbon figuredrgps to about 0.8 "Ifthecatalyst age or the Sam catalrs 'aver es OO'hOu he rate of carbonformatiQ i drops to about 014 grain. Again, for a giy' I poi ted out,the r creases with increase hydrogen partial pres.- sure in the system.Thusat acatalyst 'ajge aver.- ag lg ,flu ls und r s fnth si d iq s nd rt tine und r hrdrqen' na tia r s i o ab t n i e syr h i r ac p c b n wasdeposited at the rate of about i. 3"grams'.per cubic meter ..of- H 2.-|-CQ consumed] Operating at 189p. .s'. i. reducedthis figure to 1.0 grams,and a 9 to client cream:

Unfortunately, desirable sea is to keep carbon ma te at a 163 rat i 1 ben fdvind h t erl i e. rate Q a bbn i w ti nal b end e eerfdewn th i ldof use ul n h s s ro u ts dficoi versi ly; those Op a n cond t ons wh cha e ishyieids o 0 h j ca bons a o aro forma xces ire am unt bf a' bcn;Thu

as indica ed; whe th lhydi gen a i 'p s r i th s n hesis feed, ga is inceat to say above 209' p. i by raising the ratio of hydro- 'e catalyst,as it has been of carbon formation .de-.

e al; hat h'bI ia d s a o in ow gen in the feed, the selectivity toliquid hydrocarbons of the gasoline range is generally low. Similarly,if as a result of feeding fresh feed and recycle tail gas, the ratio ofhydrogen to the total water gas constituents of the gas feed, or H2/H2+CO+CO2 ratio, is low, the selectivity to useful products is high,but the rate of carbon formation also is excessive. Again, as has beenpointed out, fresh catalyst is highly reactive, but tends to form largequantities of carbon whereas, under the same reaction conditions, agedcatalyst produces less carbon but also less 04+ oil.

It is, therefore, the principal object of the present invention toprovide an improved process for the conversion of CO and Hz to form highyields of normally liquid hydrocarbons without forming excessive amountsof carbon during the conversion and without excessive fragmentation ofthe catalyst.

Another object of the invention is to provide means for increasing theflexibility of this rocess ,With respect to the increasing age of thecatalyst.

Other objects and advantages will appear hereinafter.

It has now been found that high yields of useful synthesis productsunaccompanied by excessive carbon formation and catalyst disintegrationmay be obtained by operating a hydrocarbon synthesis plant comprising aplurality of synthesis reactors, in such a manner that the compositionof the feed gas to each fluid catalyst synthesis reactor isadvantageously adjusted to the average age of the catalyst within saidreactor. This is accomplished by operating a plurality of fluidsynthesis reactors in parallel, each reactor being charged with catalystof different average age, combining product and unreacted gases, andadjusting the recycle ratio of tail gas to fresh feed individually toeach reactor in such a manner that high 04+ yields are obtained in eachreactor Without excessive carbon formation and catalyst fragmentation,and maintaining the overall recycle ratio for the plant substantiallyconstant. It is known that the total feed to the synthesis reactor, thatis, the combined fresh feed and recycles stream, becomes more carbonforming as the recycle ratio is increased. This is due to the decreasein hydrogen partial pressure in the reactor resulting from theinteraction of hydrogen present in the fresh feed and in the tail gaswith the carbon dioxide formed in the synthesis reactor and recycled asa constituent of the tail gas and also to the increased dilution withmethane and other constituents of the recycle gas. As this recycle ratiois increased, therefore, the selectivity to desirable hydrocarbon in thesynthesis reactor also increases, due to this decrease in the partialpressure of hydrogen and the increase in the partial pressure of carbondioxide.

In accordance with this invention, therefore, a plurality of hydrocarbonsynthesis reactors are operated with catalyst of increasing age,starting with relatively fresh catalyst. The recycle to fresh feed ratioto each reactor is so adjusted with respect to the catalyst age thereinthat maximum quantities of 04+ hydrocarbons and minimum carbon formationoccurs in each, as described more fully below. Thus to the reactorcontaining the newest (i. e., most active) catalyst, the recycle tofresh feed ratio is lowest, in order to maintain a high hydrogen partialpressure. However, because of the activity of such fresh catalyst, evenunder this high hydrogen partial '4 pressure, reasonably high yields of04+ products are obtained. On the other hand, the recycle/fresh feedratio is highest to the most aged catalyst, since the carbon formationtendencies of the latter are low, and therefore a low hydrogen partialpressure or a low ratio of may be tolerated in such reactors withoutexcessive carbon formation. Such low ratios have the highestselectivities of C4+ oils. The recycle ratios to the intermediatereactors are so scheduled that the overall recycle ratio to the plant isconstant. Such ratio is usually determined by the compressor capacity ofthe system.

Having set forth the general nature, advantages, and objects of theinvention, the latter will best be understood from the more detaileddescription hereinafter, in which reference will be made to theaccompanying drawing which is a diagrammatic representation of a systemsuitable for carrying out a preferred embodiment of the invention.

Referring now in detail to the drawing, [0, 20, 30, and 40 representsynthesis reactors preferably in the form of vertical cylinders havinglower conical sections and upper expanded sections. Fresh feed gasmixture comprising H2 and CO in the ratio of about 1.0 to 2.0 mols H2per mol CO is fed, for example, at the rate of about million standardcubic feet per day, through line 50 and is introduced into reactors I0,20, 30 and 4| through lines 12, 22, 32 and 42 respectively, and flowsupwardly through screens or grids I4, 24, 34 and 44 to effect good gasdistribution. Also introduced into the synthesis reactors is recyclegas, as described more fully below.

The reactors contain a finely divided iron group metal catalyst,preferably an iron-type catalyst having a particle size range of about10-200 microns, preferably 20-100 microns. The catalyst is fluidized bythe upfiowing gasiform reactants and reaction products to form a densehighly turbulent mass, having a well-defined upper level and an apparentdensity of about 30- fiuidization of the type of catalyst employed,-

which may be sintered reduced pyrites ash, or ammonia synthesis catalystor the like, prefer?- ably promoted with 0.51.5% K2003. These linearvelocities may be maintained at the same rate for each reactor, or theymay be varied in accordance with the age of the catalyst as detailedbelow.

The catalyst is so arranged in the reactor that the catalyst in reactorsI0, 20, 30 and 40 have had an average age or number of hours undersynthesis conditions, for instance of 350, 1050, 1750 and 2450 hoursrespectively.

Within the reactors the total pressure is adjusted to about 250 to 750p. s. i. g., and suitable temperatures of about 550 to 750 F. are main-'tained by any conventional cooling means, such as cooling coils.

Gasiforin reaction products are withdrawn overhead from the reactorsthrough gas-solid separators, such as cyclones I6, 26, 35, and 46, andthrough lines I8, 28, 38 and 48 respectively, cooled in cooler 52, andpassed through line 54 to a liquid-gas separator 56. Water and oil arewithdrawn downwardly from separator 58 through line 58 to be furthertreated by conven-' aisseiser tion'al separation andproductrecovery-means (not shown)'-.

Tail gas is passed? overhead from separator tfi through line -60."It-may; if desired, be-passed through caustic scrubber 62, foradjustment-f its carbon dioxide content, before being-passedtorecyclepump 64, or it may by-pass scrubber 62 and: bepassed directly -"to'-pump 6 1; through" bypass line 06; Also; if'des'ired, a portionof thetail gas may be removed from the'systemthrough line 68.

200- million standard cubic' feet per day; to the reactors as recyclegas; Val-ves 12, 14,46 and 'Hl'areso adjusted that the' ratio "ofrecycle-to fresh f eed-isproporti onecl in accordance -withthe age ofthe catalyst within therespectivereactors. Recycle tail gas enters'therespective-reactor feed inletlines through lines-80; 82 84 and 8trespeetive1y.- Thus the tailgas which may have acomposition of Ha/CO/COzof about 1.5:0.1:1 is-'-re"-- cycled through line Sit toreactor lllwhich contains the newest and most active catalyst in'the' ratio ofabout 0 to 1- part recycle to lpartfresh' ratio in the feed gas of:0.2'-to..0.6, under. which conditions high. 04+ selectivities are favored.Intermediate reactors and are provided with recycle/fresh feed ratio ofintermediate values, such as 0.2 to 3 and 0.5 to 5, respectively. Thetotal overall recycle ratio to the plant, however, is determined by thecapacity of recycle pump 64 and may be 0.3 to 3.

The invention admits of numerous modifications obvious to those skilledin the art. Thus it may be desirable to vary the temperature levelsmaintained in the reactors, with reactors containing more aged catalystsbeing at higher temperature levels than those containing newercatalysts. Catalysts may be withdrawn from reactors i0, 20, 30 and 40 asdesired through lines 88, 90, 92 and 9E. The reactors need not all be ofthe same volume, but it may be advantageous for the reactors containingthe more aged catalysts to have larger volumes than the others, so thatthey may contain more catalyst. In such case, the reactor receiving thefresh catalyst would always be the smallest vessel and would operate atlowest recycle ratio. It may be desirable, depending upon thecircumstances, to carry out the operation by maintaining a givenconversion level in each reactor, or to make the recycle to fresh feedadjustment to operate at a given rate of carbon formation. Also, ascatalyst ages to an extent that satisfactory conversions, even at thehigh recycle ratios, are no longer obtained, it may be discarded orregenerated, and the cycle continued by replacing the discarded catalystwith fresh catalyst, and the recycle ratios readjusted all along theline accordingly. Also, any number of reactors may be employed.

Therefore, in accordance with the above invention wherein by means ofadjusting the recycle ratios to a plurality of synthesis reactors inaccordance with the age of the catalyst therein,

From recycle-pump 64 th'e tailgasis pumped through line 10 say at therate-0f about so {that operation -is-maintained within the re actors atas low a hydrogen partial pressure'aS is consistent with a reasonableamount of carbon formation, a process has been described wherein goodyields of valuable synthesis products are ob-'- tained whileunaccompanied by excessive carbon formation and fluid catalystdisintegration.

The invention may be further illustratedbythe following example.

In a synthesis operation using an iron catalyst at 650"F. thecomposition of the-fresh fe'e'd' (synthesis gas) and the dry exit gasused for recycle had thefollowing compositions in mo'l percent':

part of fresh feed, giving a mixed feed-contain ing 53% Hz;

one reactor is being charged every 700 hours, the

arithmetic average ageof catalyst-in the' four .reactors would .be-350,1050, 1750 and 2 l50ho'urs,

respectively. In order to adjustcarbon forma tion anddisintegrationtendencies to be equal in each reactionvessel' and therebytoihold the over---' all carb'on formation for agive'n: overall yieldto! a minimum, it is necessary to operate with catalyst of the abovenamed ages at Hz partial pressures of 215, 191, and 168 p. s. i.,respectively. In order to obtain these H2 partial pressures with gaseshaving the compositions given above, it is necessary to use recycleratios to the four reactors of 0.4, 1.3, 3.0 and 5.0, respectively. Theabove figures are recapitulated in the following If the four reactorsare of the same diameter and the diameters are set to operate with aminimum velocity of 0.35 ft./sec. in the A reactor, it will be seen fromthe above tabulation that if an equal quantity of fresh feed is fed toeach reactor the velocity to the D reactor, having the highest quantityof recycle gas, will be 1.5 ft./sec. It is known in the art that thesetwo extremes, 0.35 and 1.5 ft./sec., are both Within the workable range.The last column in the above tabulation shows the fraction of Hz in thewater gas constituents of the total, mixed feed gas. This ratio combinedwith the catalyst age is important in fixing the selectivity or yield ofheavier hydrocarbons per unit of gas consumed. It will be seen that inthe above operations this quantity does not vary widely and that wherethe quantity is highest (conducive to lowest se- Fresh Recycle:

Irrasmuch as thesynthesis-section: was operatedat 400 p. s. i. g.=pressure, thepartial pre'ssure of H 2 was about 180 p. -s. i. In a plantconsisting of four reactors containing catalystof varying ages, if thecatalyst is usedtor-a total of 2800 hours before 'beingdiscarded and thecharging of the four reactors'is so scheduled that leetivity) thecatalyst is freshest and will therefore tend to compensate for the lessfavorable gas composition. Furthermore the composition most conducive togood selectivities is fed to the catalyst having the greatest age whereexcessive carbon formation and wax formation commonly associated withfeed gases low in H2 content are least apt to occur.

What is claimed is:

1. An improved process for producing high yields of valuable conversionproducts from H2 and CO in a fluid catalyst hydrocarbon synthesisprocess without causing excessive deposition of carbonaceous materialwhich comprises passing fresh synthesis gas in the ratio of about 1 to 2mols of hydrogen per mol of carbon monoxide simultaneously into aplurality of hydrocarbon synthesis reaction zones, maintaining in saidzones dense fluidized beds of iron-type catalyst, maintaining in saidhydrocarbon synthesis zones, catalysts of age such that the averagecatalyst age in any one zone differs from that in any other zone andwherein the catalyst in one of said zones is relatively fresh,maintaining a total pressure in each of said zones in the range of about250 to 750 pounds, withdrawing product comprising tail gases from saidzones, combining said tail gases, recycling at least a portion of saidtail gas separately to each of said synthesis zones, the ratio ofrecycle tail gas to fresh feed to the synthesis zone containing thefreshest catalyst being substantially lower than the ratio of recycletail gas to fresh feed supplied to the synthesis zone containing themost aged catalyst, which last-named ratio is also higher than the ratioof recycle to fresh feed fed to synthesis zones containing catalyst ofintermediate age, which ratios in turn are higher than the recycle tofresh feed ratio to said zone containing the freshest synthesiscatalyst, whereby the hydrogen partial pressures and the Hz/H2+CO+CO2ratios in each of said zones is maintained responsive to the catalystage in said zone and whereby high yields of valuable conversion productsand low quantities of carbon within said respective synthesis zones areformed.

2. The process of claim 1 wherein the total pressure in each of saidzones is about 400 p. s. i. g.

3. The process of claim 1 wherein the temperatures maintained withinsaid respective synthesis zones increases with, and. is a directfunction of, the catalyst age.

4. The process of claim 1 wherein the recycle ratio increases by stepsas the catalyst ages.

5. The process of claim 1 wherein the overall ratio of recycle tail gasto the fresh feed remains substantially constant.

6. The process of claim 1 wherein the ratio of recycle to fresh feed .tothe synthesis zone containing the newest catalyst is in the range of 0.2to 1.0.

7. The process of claim 1 wherein the ratio of recycle to fresh feed tothe synthesis zone containing the most aged catalyst is in the range of1.0 to 5.0.

ALEXIS VOORHIES, JR. ROBERT W. KREBS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,271,259 Herbert Jan. 27, 19422,347,682 Gunness May 2, 1944 2,451,879 Scharmann Oct. 19, 19482,467,803 Herbst Apr. 19, 1949

1. AN IMPROVED PROCESS FOR PRODUCING HIGH YIELDS OF VALUABLE CONVERSIONPRODUCTS FROM H2 AND CO IN A FLUDI CATALYST HYDROCARBON SYNTHESISPROCESS WITHOUT CAUSING EXCESSIVE DEPOSITION OF CARBONACEOUS MATERIALWHICH COMPRISES PASSING FRESH SYNTHESIS GAS IN THE RATIO OF ABOUT 1 TO 2MOLS OF HYDROGEN PER MOL OF CARBON MONOXIDE SIMULTANEOUSLY INTO APLURALITY OF HYDROCARBON SYNTHESIS REACTION ZONES, MAINTAINING IN SAIDZONES DENSE FLUIDIZED BEDS OF IRON- TYPE CATALYST, MAINTAINING IN SAIDHYDROCARBON SYNTHESIS ZONES, CATALYSTS OF AGE SUCH THAT THE AVERAGECTALYST AGE IN ANY ONE ZONE DIFFERS FROM THAT IN ANY OTHER ZONE ANDWHEREIN THE CATALYST IN ONE OF SAID ZONES IS RELATIVELY FRESH,MAINTAINING A TOTAL PRESSURE IN EACH OF SAID ZONES IN THE RANGE OF ABOUT250 TO 750 POUNDS, WITHDRAWING PRODUCT COMPRISING TAIL GASES FROM SAIDZONES, COMBINING SAID TAIL GASES, RECYCLING AT LSEAST A PORTION OF SAIDTAIL GAS SEPARATELY TO EACH OF SAID SYNTHESIS ZONES, THE RATIO OFRECYCLE TAIL GAS TO FRESH FEED TO THE SYNTHESIS ZONE CONTAINING THEFRESHEST CATALYST BEING SUBSTANTIALLY LOWER THAN THE RATIO OF RECYCLETAIL GAS TO FRESH FEED SUPPLIED TO THE SYNTHESIS ZONE CONTAINING THEMOST AGED CATALYST, WHICH LAST-NAMED RATIO IS ALSO HIGHER THAN THE RATIOOF RECYCLE TO FRESH FEED FED TO SYNTHESIS ZONES CONTAINING CATALYST OFINTERMEDIATE AGE, WHICH RATIOS IN TURN ARE HIGHER THAN THE RECYCLE TOFRESH FEED RATIO TO SAID ZONE CONTAINING THE FRESHEST SYNTHESISCATALYST, WHEREBY THE HYDROGEN PARTIAL PRESSURES AND THE H2/H2+CO+CO2RATIOS IN EACH OF SAID ZONES IS MAINTAINED RESPONSIVE TO THE CATALYSTAGE IN SAID ZONE AND WHEREBY HIGH YIELDS OF VALUABLE CONVERSION PRODUCTSAND LOW QUANTITIES OF CARBON WITHIN SAID RESPECTIVE SYNTHESIS ZONES AREFORMED.